This application is related to and claims priority from Japanese Patent Applications No. 2001-113082 filed on Apr. 11, 2001, and No. 2002-32345 filed on Feb. 8, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel cell system having a fuel cell that generates electric power by an electrochemical reaction between hydrogen and oxygen. The fuel cell system is suitably used for a movement body such as a vehicle, a ship and a portable generator.
2. Description of Related Art
In a fuel cell for generating electrical power using a chemical reaction between hydrogen and oxygen, heat is generated due to the chemical reaction. Therefore, the fuel cell is need to be maintained at a predetermined temperature (e.g., about 80xc2x0 C.) for improving power generation efficiency. For example, heat generated due to the chemical reaction is radiated to atmospheric air by using a radiator through cooling water. Although a heat generation amount in the fuel cell is small, a heat radiation amount due to exhaust gas is small. Accordingly, a heat radiation amount in the radiator using cooling water is increased. Further, since a temperature difference between cooling water and atmospheric air is small, a cooling operation using the radiator is not effective. Thus, in order to sufficiently cool the fuel cell only using the radiator, it is need to increase the size of the radiator.
In view of the foregoing problem, it is an object of the present invention to provide a fuel cell system which increases a cooling capacity for cooling a fuel cell by using an evaporation latent heat of water in the fuel cell in addition to a radiator.
According to the present invention, in a fuel cell system having a fuel cell that generates electrical energy by an electrochemical reaction between hydrogen and oxygen, a heat-generation amount detection device is provided for detecting a heat generation amount in the fuel cell, and an evaporation amount controller controls an evaporation amount of water in the fuel cell based on the heat generation amount detected by the heat-generation amount detection device. Accordingly, the fuel cell can be cooled using the evaporation latent heat of water in the fuel cell by adjusting the evaporation amount of water in the fuel cell. Thus, a cooling load in a radiator for cooling the fuel cell can be reduced, thereby reducing a size of the radiator.
Preferably, the heat-generation amount detection device is an electric-power detection device for detecting an electric power output from the fuel cell. When the electric power detected by the electric-power detection device is larger than a predetermined value, the evaporation amount controller increases the evaporation amount of the water in the fuel cell. Alternatively, the heat-generation amount detection device is a current detection device for detecting a current output from the fuel cell. Further, when the current detected by the current detection device is larger than a predetermined current, the evaporation amount controller increases the evaporation amount of water in the fuel cell. Accordingly, an increase of the heat-generation amount can be indirectly detected, and the evaporation amount of the water in the fuel cell can be suitably controlled.
Alternatively, the heat-generation amount detection device is a temperature detection device for detecting a temperature of the fuel cell. Further, when the temperature detected by the temperature detection device is higher than a predetermined temperature, the evaporation amount controller increases the evaporation amount of water in the fuel cell. Accordingly, the increase of the heat generation amount can be directly detected, and the evaporation amount of the water in the fuel cell can be suitably controlled.
Preferably, the evaporation amount controller is a humidification amount adjuster for adjusting at least one humidification amount of hydrogen and oxygen to be supplied to the fuel cell. In this case, the evaporation amount of water in the fuel cell can be increased, when the humidification amount adjuster reduces the humidification amount. Alternatively, the evaporation amount controller is at least one of a hydrogen pressure adjuster for adjusting a pressure of hydrogen to be supplied to the fuel cell, and an oxygen pressure adjuster for adjusting a pressure of oxygen to be supplied to the fuel cell. In this case, the evaporation amount of water in the fuel cell can be increased by reducing at least one of hydrogen pressure using the hydrogen pressure adjuster, and oxygen pressure using the oxygen pressure adjuster. Alternatively, the evaporation amount controller is one of a hydrogen-flowing amount adjuster for adjusting an amount of hydrogen to be supplied to the fuel cell and an oxygen-flowing amount adjuster for adjusting an amount of oxygen to be supplied to the fuel cell. In this case, the evaporation amount of water in the fuel cell can be increased by increasing at least one of a hydrogen amount using the hydrogen-flowing amount adjuster, and an oxygen amount using the oxygen-flowing amount adjuster.
According to the present invention, the fuel cell system includes water-amount determining means for determining a water amount in the fuel cell, and cooling determining means for determining a need of cooling in the fuel cell based on the heat generation amount detected by the heat-generation amount detection device. Further, when the cooling determining means determines that the fuel cell is need to be cooled, and when the water-amount determining means determines that the water amount in the fuel cell is sufficient, the evaporation amount controller increases the evaporation amount of water in the fuel cell. Accordingly, the cooling capacity of the fuel cell system can be effectively improved, while operation efficiency of the fuel cell system is improved.